1. Field of the Invention
The present invention relates to a synchronization control device, and more particularly, to a synchronization control device which is used in the control of machines having operating parts, such as machine tools, industrial machinery, robots, and the like.
2. Description of the Related Art
In the control of machines having operating parts, such as machine tools, industrial machinery, robots, and the like, there are cases where a plurality of operating members are controlled in a synchronized fashion. In synchronization control of this kind, a method of synchronization control is known in which the plurality of operating members are divided between a drive side and a driven side, and the positional control of members on the driven side is made to correspond to the position data of the members on the drive side. Synchronization control of this kind frequently uses electronic cams, the driven-side members being provided with a drive mechanism, such as a servo motor, and the position of the drive mechanism being controlled in accordance with position data for the drive-side member. With this synchronization control, the driven-side members operate in synchronism with the drive-side members.
FIG. 8 is a general schematic drawing for illustrating synchronization control according to the prior art. In FIG. 8, the driven side 2 is driven by a servo motor 4 on the basis of a movement command from a control device 6. The control device 6 internally stores a positional relationship between members on the drive side 1 and the driven side 2 when the members are operating in synchronism in a displacement table TD, determines the positional data of the position of the member on the driven side 2, which corresponds to the position of the member on the drive side 1, at prescribed intervals apart, from the positional relationship stored in the displacement table TD, sends a movement command to a member driving servo motor 4 on the driven side 2, on the basis of this positional relationship, and thereby controls the position of the member on the driven side 2. Thus, it is possible to achieve synchronization between the drive side 1 and the driven side 2.
FIG. 9 is a diagram showing a state of synchronization of a driven shaft in a synchronization control device according to the prior art. The vertical axis represents the displacement PA of the driven shaft, and the horizontal axis represents the phase PH of the drive shaft. The curve in FIG. 9 illustrates the displacement table TD which indicates the relationship between the phase of the drive shaft and the displacement of the driven shaft, for each phase of the drive shaft. PW indicates a driven shaft standby position, and the driven shaft waits at standby at this position before synchronization. Furthermore, DA indicates a permitted movement amount, which indicates a range in which synchronization is possible from the driven shaft standby position PW. In a synchronization control device set up in this way, when the driven shaft, which is stopped at the driven shaft standby position PW, is synchronized with the drive shaft at an intermediate stage, then synchronization is started when the amount of movement of the driven shaft has reached the permitted movement amount DA, and synchronization is performed on the basis of the displacement table TD.
Japanese Patent Application Publication No. 2002-202818 discloses technology wherein, when driving of a driven side member is started and synchronized with the operation of a drive side member, movement of the driven side member is started before a synchronization start position for starting synchronized operation, the drive side member and the driven side member are synchronized at the synchronization start position by acceleration/deceleration control, and positional control is performed on the basis of a displacement table, from synchronization start phase on.
FIG. 10 is a diagram showing a state of synchronization of a driven shaft in the synchronization control device disclosed in Japanese Patent Application Publication No. 2002-202818. Parts of the configuration which are similar to FIG. 9 are labelled with the same reference numerals and description thereof is omitted here. In FIG. 10, movement of the driven shaft is started at a movement start phase PHS1 before the synchronization start phase PHS2, acceleration/deceleration control is performed during the time period from the movement start phase PHS1 to the synchronization start phase PHS2, and synchronization is performed in the synchronization start phase PHS2.
In the synchronization method described in the prior art, synchronization is started when the amount of movement of the driven shaft has become equal to or less than the permitted movement amount DA. On the other hand, since the movement of the drive shaft is read out on the basis of a monitoring period, then when the drive shaft moves at high speed, there is a risk that the amount of movement of the driven shaft may not be within the permitted movement amount DA at the time that it is monitored, and that synchronization may not be possible. One method for avoiding this would be to set the permitted movement amount DA to a large value in accordance with the highest speed of the drive shaft, but if the permitted movement amount DA is set to a large value, then the amount of movement of the driven shaft during synchronization also become large, accordingly, and hence there is a risk of causing large shocks to the machinery during synchronization.
Furthermore, in the technology disclosed in Japanese Patent Application Publication No. 2002-202818 and illustrated in FIG. 10, during the time period in which acceleration/deceleration control is performed from the movement start phase PHS1 to the synchronization start phase PHS2, the driven shaft performs movements that are different to those based on the displacement table TD, and hence there is a risk of interference with other driven shafts.